1. Field of the Invention
This invention relates to a fuel injection pump equipped with a pre-stroke varying mechanism used in diesel engines or other internal combustion engines, and particularly to a fuel injection pump which is able to prevent cavitation erosion due to spillage of high-speed, high-pressure fuel into the fuel reservoir chamber.
2. Description of the Prior Art
Conventional fuel injection pumps are provided with pre-stroke varying mechanisms used to vary their pre-strokes, and typically the pre-stroke is varied by adjusting the relative positions of a vertically-reciprocating plunger and a timing sleeve which mates to the outside of the plunger. For example, Japanese Utility Publication No. 62(1987)-8381 and others may be cited.
Cavitation erosion occurring in the pump housing of such a fuel injection pump 1 equipped with such a pre-stroke varying mechanism is described in Japanese Patent Publication No. 55(1980)-93959, Japanese Patent Publication No. 57(1982)-59054, Japanese Utility Publication No. 58(1983)-109554 and others.
Furthermore, in the fuel injection pump of Japanese Utility Publication No. 61(1986)-167469 in which a cavity is formed on the plunger barrel to prevent cavitation erosion, the spilled high-pressure fuel is assumed to be forced to collide with only the plunger barrel so that the cavity cushions this high pressure. Therefore, although the pump itself may be protected, protection of the plunger barrel is difficult.
Here follows a description of cavitation erosion which occurs in the plunger barrel located on the outside of the timing sleeve and the pump housing, made with reference to FIGS. 4 through 6.
FIG. 4 is a vertical cross section through a portion of a fuel injection pump 1 in which the same number of vertical holes 3 as the number of cylinders in the engine are formed in its pump housing 2. A plunger barrel 4 is inserted into each vertical hole 3 and secured with anchor bolts 5. A plunger 6 is inserted into the plunger barrel 4 such that it is capable of rotary and reciprocating motion.
As shown in FIGS. 5 and 6, a fuel reservoir chamber 8 is formed within the plunger barrel 4 by providing open windows 7 on the left and right, perpendicular to the length of the plunger barrel 4. This fuel reservoir chamber 8 encloses a timing sleeve 9 able to move vertically within it. This timing sleeve 9 mates to the outside of the plunger 6 such that it is positioned between the plunger 6 and the plunger barrel 4. The fuel reservoir chamber 8 is continuously supplied by a fuel supply pump 11 with fuel from a fuel tank 10.
A delivery valve 12 is provided within the plunger barrel 4 above this plunger 6, and the space between this delivery valve 12 and the plunger 6 forms a fuel pressure chamber (plunger chamber) 13. Furthermore, a fuel outlet 15 is formed in a delivery valve holder 14 above the delivery valve 12, and connected via a fuel injector 16 to a fuel injection nozzle 17.
In addition, the lower edge of the plunger 6 is in contact with a cam connected to the engine (both not shown) so that it is made to reciprocate vertically in the diagram with the rotary motion of the engine.
Furthermore, a driving face (not shown) is formed on the lower portion of this plunger 6, and this driving face engages an injection quantity-adjusting sleeve 18. By rotating this injection quantity-adjusting sleeve 18 with an injection quantity-adjusting control rack 19 connected to an accelerator pedal (not shown), the plunger 6 is rotated to change the engagement position of a control lead groove 27 and cutoff hole 30 (to be described hereafter), thereby changing the effective stroke of fuel delivery under pressure, and thereby adjusting the quantity of fuel injected.
Formed in the timing sleeve 9 are a vertical guide groove 20 in the right center of FIG. 4 and a lateral engaging groove 21 in the left center of FIG. 4, respectively. A guide pin 22 provided on the plunger barrel 4 engages the guide groove 20, while a control rod 23 is inserted into the engaging groove 21.
This control rod 23 is inserted through a lateral hole 24 formed in the pump housing 2 and is rotatably supported by the pump housing 2 with bearings (not shown). The control rod 23 is linked to a step motor or other actuator (not shown) and driven by the actuator based on the engine speed or other detected signal.
Thus, the pre-stroke may be adjusted by moving the timing sleeve 9 vertically with the control rod 23. To wit, the pre-stroke of the plunger 6 is defined to be its distance of travel from the lower edge of the timing sleeve 9 to a fuel suction and exhaust hole 25 (to be described later) at the bottom dead center position of the plunger 6 or the distance of travel from the bottom dead center position of the plunger 6 until the fuel suction and exhaust hole 25 closes, so that fuel injection begins when the fuel suction and exhaust hole 25 is closed.
Furthermore, in FIG. 4, when the plunger 6 slidably inserted into the plunger barrel 4 is driven by the rotary motive power of the engine so that it reciprocates within the plunger barrel 4, fuel within the fuel reservoir chamber 8 is sucked into the fuel pressure chamber 13 and then the fuel within this fuel pressure chamber 13 is delivered under pressure from the fuel outlet 15 through the fuel injector 16 and injected from the fuel injection nozzle 17.
To wit, this plunger 6 is provided with this radially-oriented fuel suction and exhaust hole 25 which acts as a fuel inlet port open to the fuel reservoir chamber 8, a connecting hole 26 formed to connect this fuel suction and exhaust hole 25 and the fuel pressure chamber 13 in the central axis direction, the control lead groove 27 formed at an inclination on its outer surface, and a connecting vertical groove 28 which serves to connect this control lead groove 27 and the opening of the fuel suction and exhaust hole 25. Note that an auxiliary hole 29 may also be provided on the plunger 6 in the radial direction to connect the top of this connecting vertical groove 28 to the connecting hole 26.
Furthermore, a cutoff hole 30 which acts as a spill port is formed in a radial direction completely through the timing sleeve 9 which slidably mates to the outside of the plunger 6. This cutoff hole 30 is disposed in such a vertical position that it is able to connect to the control lead groove 27 in response to the vertical motion of the plunger 6.
In this configuration, when the plunger 6 first rises from its bottom dead center position, the fuel suction and exhaust hole 25 opens to the fuel reservoir chamber 8 so that this fuel reservoir chamber 8 is connected to the fuel pressure chamber 13 by the fuel suction and exhaust hole 25 and the connecting hole 26, so the pressure of the fuel in the fuel pressure chamber 13 does not rise and the delivery valve 12 remains closed.
To deliver fuel, the plunger 6 rises and the pressure of the fuel within the fuel pressure chamber 13 increases as the fuel suction and exhaust hole 25 is closed by the timing sleeve 9, at which time, the delivery valve 12 opens to deliver fuel from the fuel outlet 15 and injection (delivery of fuel under pressure) begins.
As the plunger 6 rises further, the control lead groove 27 connected to the fuel suction and exhaust hole 25 connects to the cutoff hole 30 in the timing sleeve 9, causing the cutoff hole 30 to be connected to the fuel pressure chamber 13 through the cutoff hole 30, the control lead groove 27, the connecting vertical groove 28 and auxiliary hole 29 and the connecting hole 26, so that fuel in the fuel pressure chamber 13 flows back to the fuel reservoir chamber 8, lowering the fuel pressure within the fuel pressure chamber 13, and then the delivery valve 12 closes and injection (delivery of fuel under pressure) ends.
However, when this fuel sprays, or rather, spills so that it flows back into the fuel reservoir chamber 8, the flow of high-speed, high-pressure fuel is suddenly released and collides with the inside wall 4A of the plunger barrel 4, and the flow is then redirected along the inside wall 4A so that it collides with the inside wall 2A of the pump housing 2 at an angle of collision AN (refer to the arrow in FIG. 6). Therefore, the problem of cavitation erosion (hereinafter called simply "erosion") E (indicated by groups of dots in FIG. 6) occurs in which the surfaces of the inside walls 4A and 2A are worn or damaged by repeated generation of bubbles by negative pressure and their subsequent collapse due to the next fuel pressure wave.
Note that as shown in FIG. 6, both the distance D1 from the cutoff hole 30 to the inside wall 4A of the plunger barrel 4 and the distance D2 from the point at which fuel sprayed from the cutoff hole 30 collides with the inside wall 4A to inside wall 2A of the pump housing 2 are short distances over straight lines.
Moreover, there are restricting areas 31 between the inside wall 4A of the plunger barrel 4 and the peripheral surface of the timing sleeve 9; these restricting areas 31 cause the fuel pressure to rise, resulting in the fuel colliding with the inside walls 4A and 2A at higher speeds and higher pressures, increasing the effect of these collisions and promoting the occurrence of the erosion E described heretofore.
Thus, there is a problem in that the occurrence of erosion E as such reduces the durability of the pump housing 2 and plunger barrel 4.